The use of immunocytochemical techniques for the detection of steroid hormones in breast cancer cells

Indirect immunofluorescence and immunoperoxidase assays were developed to detect estradiol and progesterone in breast cancer cells. Appropriate controls were used to confirm immunologic specificity. Studies of estradiol binding by human breast cancer cells identified three groups: no detectable binding (25%); all tumor cells exhibiting binding although to different degrees (4%); and tumors with varying numbers of positive and negative cells (71%). Similar observations were made with respect to progesterone binding. The percentage of cells with estradiol binding was correlated with the amount of estrogen receptors (ER) present in the tumor specimens. Post-hormone binding events e.g., nuclear binding of estradiol, were also evaluated. Some tumor cells showing cytoplasmic binding of estradiol did not show nuclear binding of estradiol; such tumors lacked detectable diethylstilbestrol under routine assay conditions, and relatively high concentrations of estradiol were needed to observe estradiol-specific staining. The results suggest that the immunocytochemical assays detect hormone-specific binding, but that the binding is probably due to multiple classes of steroid-binding sites.